Lumber edgers saw off the rough side edges of freshly sawn lumber (planks), also referred to as flitches, to produce 4 sided boards using edger saws. The edger saws are parallel to each other and typically about 4″, 6″, 8″, 10″ or 12″ apart. The flitch is scanned prior to cutting to determine what the widest and longest single board or set of side by side boards that can be manufactured, then laterally positions and skews the flitch to suit that cut solution and releases it to be conveyed linearly through the edger saws.
Lumber edgers can be categorized as gang or shifting edgers. In gang edgers the edger saws remain stationary. In a shifting edger the edger saws can move left or right independently of one another. This allows setting the saws to best maximize the product that can be produced from a particular position of the lumber. In this usage, position means the side to side translation of the board relative to a pair or bank of saws such that as the board is propelled through the saws a particular path is sawn. Additionally, position includes the rotation of the board or skew relative to the same pair or bank of saws. Combining the translation and skew forms the position of the flitch.
Modern lumber edgers usually include a lumber sensor that measures the dimensions of the lumber (flitch). The lumber is then positioned in relation to the edger saws to maximize the amount of board that can be produced by cutting the edges. Present day positioning systems consist of multiple positioning assemblies called fetchers. Two positioners will be used on each board, a near-end positioner and a far-end positioner. By setting at differing positions around the centerline feed of the edger feed table, they can “skew” the piece laterally in relation to the saws. These fetchers are most often powered by hydraulic cylinders, with servo/proportional valves for accurate sets and temposonics style probes for positioning feedback to the controls system.
Hydraulic systems are not as desirable in a sawmill setting as they once were. Fire, EPA reguations, over-heating, high horsepower requirements, maintenance problems and constant leaks are just a few of the problems relating to these systems.
A lumber edger is described in my previous published U.S. patent application No. 2013/0269836, filed 11 Apr. 2013, which is incorporated herein by reference.